Snapping Bones to Bones (In Other Armature)
I was looking for the same. I saw the UE folks do this and was trying to do it without their plugin. They show it happening here... (https://www.youtube.com/watch?v=F9cTXzO8wq0&amp;list=PLZlv_N0_O1gaxZDBH0-8A_C3OyhyLsJcE&amp;index=4&amp;ab_channel=UnrealEngine)
It's a bit tricky since your cursor has to be in the correct place...

In object mode, select both armatures.
Go into 'Edit mode'
Enable 'Vertex Snapping' (refer to image below to see where to find the button to open the menu. (enable rotation/scale here if you'd like to)
Select the bone head/tail that you would like to move to the other.
** Tricky Part here: Ensure your cursor is inside (or near) the source head/tail before you start transforming.
Press G to transform the position of the tail/head.
Moving close to the other armature tail/head should snap to it.

** Also note that, if you move the tail of one bone, you will likely have to move the head of it's connected bone too.